Montserrat Volcano Observatory

Daily Report
Report for the period 4 pm 15 July
to 4 pm 16 July 1997

The alert level system has been revised by zones

Activity at the volcano has been at about the same level as yesterday. The seismicity is dominated by rockfalls signals.

No clear views were obtained of the volcano due to very overcast conditions throughout the day. Several fresh rockfalls were noted on the eastern face of the dome by a GPS field team. Minor rockfalls, which extended up to 500 m from the dome, were also observed in Tuitts and Mosquito Ghaut. Steam was observed emanating from a very localised area in the Belham Valley at about 9:30 am today, immediately following the heavy rains during the early morning. The steaming, which occurred in a steep sided part of the valley below Molyneux, is believed to be due to small scale slumping which enabled the interaction of rainwater with hot pyroclastic deposits.

The number of rockfall signals is less than yesterday with 35 events being recorded. One long period earthquake was also recorded. The seismic stations recorded 3 very high frequency events which are felt to have been caused by the thunder generated by the early morning thunder storm. There has been a slight increase in the level of tremor on the St George's Hill seismic station since about 11:00 am today. This is most likely due to increased steaming due to the morning rainfall.

The EDM line between Waterworks and Lees Yard was again surveyed twice today. The data collected from these stations has not shown any changes since they were first established on 8th July, 1997. A GPS survey of the entire volcano, including stations at Long Ground, Whites, Harris, Windy Hill, St George's Hill and Lees Yard, was completed using the helicopter today. The results from this survey has not yet been processed.

There has been a very slight increase in the amplitude of the Chances Peak tiltmeter during the past 24 hours. One very low amplitude peak was recorded by the tiltmeter during the period with a continuation in the long term trend.

Although there appears to be very little seismic activity from the volcano, there have been periods in the past when the dome has continued to grow with few earthquakes apart from rockfalls. Thus it is probable that material is currently building up above Gages wall and Mosquito Ghaut, and the potential for large pyroclastic flows onto the northern and western flanks into the Central corridor and Plymouth is significant.

Residents should note that pyroclastic flow and ash eruptions have occurred during the past week with no direct association with seismicity or tiltmeter readings. This means that people entering the designated exclusion zone put themselves at extreme risk. People in the northern and central zones should stay alert and listen to Radio Montserrat. The current area of activity in the crater makes Mosquito Ghaut and Gages valley the most likely pathways for pyroclastic flows, but further flows in Tuitt's, Tar River or White River are possible as well.

The Belham River valley is also an area for anxiety over safety. It may provide a pathway for further pyroclastic surges and there is also a risk of hot mudflows which may form rapidly if there is a period of heavy rain. Mudflows travel extremely fast and may be near boiling point, they may extend much further along the Belham River valley than the pyroclastic surges. The pyroclastic flow and surge deposits will remain extremely hot for several days. Residents must not approach, attempt to handle or walk on the deposits because of the risk of severe burning. Residents and workers are also reminded to wear a dust mask when there is ash in the air.

Montserrat Volcano Observatory